Bull sharks on 'collision course' with humans

Amy Remeikis

Bull sharks are being forced into the Gold Coast’s canals and waterways through the destruction and modification of natural waterways.

A three-year Griffith University study tracking the habits and preferences of neonates (pups) and juvenile bull sharks in the Nerang River found that the sharks overwhelmingly preferred to use the natural waterways as their nursery ground.

But the study also found that the destruction of the natural river system, through the creation of canals and other artificial waterways, was forcing the sharks to utilise manmade habitats as they grew older, bringing them closer to where people live and play.

As the Gold Coast has grown, so too has the canal and lake system that now stretches to nearly 200 kilometres.

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Griffith University shark researcher, Dr Jonathan Werry, said the increasing popularity of coastal areas and the modification of the sharks' natural habitat were putting people and sharks on a “collision course”.

He said the research showed that pups remained in a very defined salinity range in the top reaches of the river and only moved into the canals when the salinity matched their preferred range in the natural environment.

The sharks still preferred to inhabit the main river where they could - a preference the research team believes is linked to the natural flow of the water and increased structure and mangroves - as opposed to the conditions in artificial habitats.

“What we found was most of them still had a preference for the main river, however three individuals actually showed a preference for the deeper canals in the lower reaches of the river,” Dr Werry said.

“So what we may be doing is forcing them to have to utilise artificial habitat, which is most likely not their preferred areas, if we continue with the destruction of natural areas. That is potentially forcing them to have to rely on these manmade habitats.”

Gold Coast City Council mayor, Tom Tate, said the management of bull sharks was not high on the council’s priority list.

“The bull sharks are not on the agenda,” he said.

“I am not saying we are waiting for an attack, but when there is no problem with barking dogs, we don’t do much about it.”

However Mr Tate said the management of the city’s waterways was a priority and he had given instructions to change the council’s policy in an effort to improve the river’s health within the next two years.

“In the short and medium term future, I don’t see any additional canals being developed here on the Gold Coast,” he said, promising to investigate the Griffith University study.

“Long term, and we are talking about 20 years from now, I can’t tell you what is going to happen there.”

Bull sharks are part of the waterway lore on the Gold Coast, with long term residents quick to tell their sighting stories, however Dr Werry said it was impossible to gauge how many sharks lived in the waterways.

While many residents tell tales of close calls, the last fatal attack by a bull shark occurred in February 2003, when Bob Purcell was killed while swimming in Burleigh Lake. The 84-year-old’s death came six weeks after 23-year-old Beau Martin was killed while swimming in Miami Lake.

Bull sharks are a global species and can be found in almost every river system in south east Queensland.